1. Field of the Invention
The present invention relates generally to source-transfer switching systems and more particularly to a high-speed control arrangement and high-speed switches to control the transfer of a load from one source to another with minimal transfer delays.
2. Description of Related Art
Source-transfer systems for electrical power distribution systems provide power delivery to a load by transferring the supply of the load from a first source to a second independent source when undesirable characteristics are sensed in the first source. One type of source-transfer systems utilize relatively lower-speed control systems and mechanical switches, for example, requiring in the range of ten to several hundred cycles of the source frequency to accomplish transfer of the load between two sources. These systems are arranged to operate in a "break before make" fashion such that the current is interrupted from one source to the load before the second source is connected. Another type of source-transfer system, illustrated in U.S. Pat. Nos. 5,070,252 and 3,936,782, is utilized in a "make before break" mode to transfer a load between two sources by momentarily paralleling the sources when the sources are each viable.
Another type of source-transfer system denoted the "FasTran25" utilizes high-speed vacuum switches operated by solenoids. The "FasTran25" system is stated to accomplish transfer within approximately 24 milliseconds and is described in publication DB770-512, dated August 1998, available from Joslyn Hi-Voltage Corp. of Cleveland, Ohio.
Yet another type of source-transfer switching system commonly utilizes solid-state switches, which can also be characterized as static transfer switches. The control arrangements sample the voltage waveforms of each source to detect when transfer between the sources is necessary, e.g. sensing outages and momentary interruptions as well as voltage sags and swells based on the source supplying the load being above or below preset levels. For example, see U.S. Pat. Nos. 5,808,378 and 5,644,175.
While these arrangements may be useful and generally satisfactory for their intended purposes, the transfer systems of the prior art either require expensive solid-state switches or introduce delays in transfer times.